How many reactions will I be able to do with 25 nmole PCR primers?

Most PCR reactions use 0.1−0.5 μM primer. Assuming a maximum concentration of 0.5 μM and a reaction volume of 20 μL, each reaction will require 10 pmoles of oligonucleotide primer. For a typical 25mer oligonucleotide, 1 OD is equivalent to approximately 4 nmoles, or 4000 pmoles. Guaranteed yield for most constructs on the 25 nmole scale is 3 ODs. Therefore, with even the minimum yield from a 25 nmole synthesis, you should be able to perform 1200 PCR reactions. In summary: 3 ODs of a 25mer ≈ 12 nmoles = 12,000 pmoles = 1200 reactions.